The present invention relates to 2-hydroxy-4-methylthiobutanoic acid, an analogue of the essential amino acid methionine, commonly referred to as methionine hydroxy analogue. More particularly, the present invention relates to methionine hydroxy analogue compositions which have a substantially higher 2-hydroxy-4-methylthiobutanoic acid content than compositions reported heretofore.
Various methods for preparing methionine are known. For example, the synthesis of methionine from methyl mercaptan and acrolein involves the preparation of methylmercaptopropionaldehyde which is reacted with hydrocyanic acid to form 2-hydroxy-4-methylthiobutyronitrile which is subsequently aminated and hydrolyzed to methionine. Unfortunately, the reaction of 2-hydroxy-4-methylthiobutyronitrile with ammonia is a difficult and costly procedure requiring the use of high pressure apparatus. It was subsequently found that methionine analogues such as 2-hydroxy-4-methylthiobutanoic acid, hereinafter referred to as HMBA, are virtually as effective as methionine for nutritional uses, particularly as a poultry feed supplement. However, the crystalline form of HMBA has a melting point between 38.degree. C. and 42.degree. C. depending on the purity, rendering it susceptible to liquid-solid phase change upon storage or use at ambient temperatures.
The salts of HMBA have higher melting points than the free acid form of HMBA. The sodium, potassium, magnesium and zinc salts of HMBA have previously been disclosed since these cations are minerals which must be supplemented in animal feeds. Compositions and methods disclosed for preparing salts of HMBA with the above-identified cations teach reacting essentially stoichiometric amounts of HMBA and the hydroxide, oxide, bicarbonate, carbonate or acetate of the selected cation in aqueous solution, for example see Belg. Pat. No. 882,067 and U.K. Pat. Appl. No. G.B. 2,044,775A. However, these salts are, in general, highly hygroscopic and show poor storage stability before and after mixing with animal feeds.
It is therefore the overall object of the present invention to provide enhanced HMBA compositions having substantially higher HMBA equivalent per unit weight than the ionic salts disclosed heretofore.
It is an object of the present invention to provide enhanced HMBA compositions which are less hygroscopic than the ionic salts disclosed heretofore.
It is yet another object of the present invention to provide a method for preparing the enhanced HMBA compositions embraced by the present invention.
These and other objects, features, and advantages of the present invention will become evident to those skilled in the art from the following description.